This inventions relates generally to automatic power door operators and more particularly concerns a pneumatic power door operator suitable for positioning overhead of the driven door when used on a mass transit vehicle.
Pneumatic door operators have been utilized for a substantial period of time to open and close vehicular doors. Typically such operators employ long stroke pneumatic cylinders of conventional design, or pneumatic differential engines wherein rectilinear motion is converted to rotary motion through the use of rack and pinion gearing. Operators utilizing the long stroke piston require longitudinal overhead space approximately equal to twice the stroke or actuating movement of the cylinder. In operators using the differential engine, the relatively small rotary travel of the rack and pinion requires an extensive array of operating levers and/or force multiplying links in order to adequately operate a given door. Examples of these operators are contained in U.S. Pat. Nos. 3,858,920, 3,916,567, 2,866,442 and 2,343,316.
Recent mass transit vehicles are of streamlined design requiring construction methods which greatly reduce the available intra-structure spaces formerly utilized to house the operator. Reduced available space often does not permit installation of actuating and/or operating rods, cables, and/or other force transmitting devices.
The invention disclosed herein overcomes essentially all of the above discussed spatial limitations through the use of a rodless cylinder, thereby greatly reducing door overhead longitudinal space required for housing the operator. Rodless cylinder designs minimize longitudinal space to essentially that of the basic cylinder itself. A rodless cylinder similar to the type utilized in this invention is disclosed and claimed in U. S. Pat. No. 3,779,401 said patent hereby incorporated by reference.
A further shortcoming of presently used pneumatic power door operators for transit vehicles arises from the requirement that vehicular doors be locked to prevent unauthorized exit or entry and safe operation of the car when in motion. In the case of the aforementioned pneumatic operators of the long stroke cylinder or differential engine type, door locking is sometimes achieved through "holding" pressure in the opposite side of a cylinder during vehicular operation. As those skilled in the design and operation of transit vehicles will readily recognize, loss of pneumatic pressure with "pressure hold" operation can result in freewheeling doors and passenger hazards attendant thereto. Therefore, recent door equipment has for the most part required positive mechanical locks which do not depend on operating air pressure for maintaining the operated doors in a closed position.
The invention disclosed herein provides a novel and highly satisfactory mechanical lock of simple construction which can be actuated or deactuated by the actuating pneumatic cylinder through the application of fluid pressure to the cylinder and/or mechanically released in the case of loss of pressure and/or emergency situations.
An additional feature of the invention disclosed is the controlled force applied from the cylinder external piston to the operated door. Rodless cylinders utilize magnetic field coupling between a pneumatic piston internal of the cylinder and a magnetically coupled piston external of the cylinder. The maximum force exerted on the external piston by movement of the internal piston is termed "breakaway" force. The breakaway force is controlled to limit force applied to the operated door through mechanical coupling of the door and external piston. This construction minimizes applied door edge force allowing breakaway of the door when door movement is resisted due to objects or passengers in the door path, known as door obstructions.
Accordingly, it is an object of this invention to provide a novel pneumatic power door operator requiring a minimum of longitudinal space overhead of the operated door.
It is an additional object of this invention to provide a pneumatic power door operator wherein the longitudinal space required is limited to essentially the movement of the operated door.
It is yet further an object of this invention to provide a pneumatic power door operator wherein a positive mechanical lock is achieved through utilization of the power cylinder reaction forces.
It is a still further object of this invention to provide a pneumatic door operator having a positive mechanical lock operable by the primary actuating gear.
It is a further object of this invention to provide a pneumatic power door operator wherein cushioning of door travel is provided through controlled escape of operating air, and change in effective piston area.
It is another object of the invention to provide a power door operator for a passenger mass transit vehicle having controlled door edge force in closing due to limiting operator breakaway force.
It is further object of the invention to provide a vehicular power door operator wherein door motion and control is reestablished after breakaway by re-cycling the actuating piston in the cylinder.